| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 102 === Streptocarpus rexii (Gesneriaceae) lacks the conventional shoot apical meristem (SAM). On the other hand, unorthodox meristems form on the leaves of S. rexii, and are capable of producing lateral organs and maintaining plant’s growth. Previous researches indicated that the exogenous cytokinin (CK) treatment affected the activities of the unorthodox meristems of S. rexii. We therefore aimed to understand how CK is involved in maintaining the unorthodox meristem activity of S. rexii. In this study, I isolated the CK biosynthesis IPT gene (ISOPENTENYLTRANSFERASE) and examined their expression patterns in relation to meristem activity in the seedling of S. rexii. I also tested whether the expression levels of SrIPT genes can be altered by exogenous hormone treatments in order to understand whether SrIPTs can be regulated by major phytohormones. Five IPT homologous genes were isolated from S. rexii (SrIPTs): SrIPT1, SrIPT2, SrIPT3, SrIPT5, and SrIPT9, while SrIPT2 is perhaps a pseudogene because of the formation of a premature stop codon. Real-time PCR of the other four SrIPTs revealed that SrIPT1 mainly expressed in floral organs and SrIPT3 mainly in roots, and SrIPT5 and SrIPT9 expressed in all organs examined. Furthermore, I found the strong expression signals of SrIPT1, SrIPT5 and SrIPT9 within the unorthodox meristems (basal and groove meristems) via RNA in situ hybridization. I also discovered that SrIPT5 strongly expressed in meristem-located (proximal end) rather than no-meristem-located (distal end) lamina tissue of older leaves. These results supported the hypothesis that meristem-localized CK level is required for the maintenance of these unorthodox meristems. Exogenous hormone treatments such as auxin and gibberellin can inhibit certain SrIPTs expression but CK increase their expression instead, implying that hormone regulated SrIPTs expression may be important for meristem maintenance. Overall, our results indicated that certain CK biosynthesis IPT genes expressed in unorthodox meristems, suggesting they have a role on meristem maintenance.
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